The present invention relates to semiconductor devices provided with a photodetector and a signal processing section, more particularly to a semiconductor device for optical communication which receives an infrared signal from a transmitter and outputs a control signal for controlling operation of each electronic device, on which the semiconductor device is mounted, such as a television receiver, a video tape recorder, an audio component unit and an air conditioner.
Conventionally, a semiconductor device for optical communication has been provided with a light-receiving chip and a control IC chip on a board, some of these chips being sealed with an infrared-transparent resin.
This semiconductor device for optical communication receives a control signal for various electronic devices transmitted from a transmitter using infrared rays. This signal transmitted using infrared rays is so weak that the semiconductor device for optical communication incorporates a high-gain amplifier, which amplifies the optical signal using infrared rays, and converts the optical signal into a digital signal and outputs this signal. Accordingly, the semiconductor device for optical communication is very sensitive to noise.
As a measure against noise, the infrared transmitting resin is covered with a shield casing made of a metal. When a user mounts the semiconductor device for optical communication on a board, an end portion of the shield casing is electrically connected to a GND terminal of the board, with the result that noise is eliminated.
However, the following problems (a)–(c) have been found:
(a) There is an increase in the number of processes required for covering the device with the shield casing.
(b) There is a cost for the shield casing itself.
(c) There is a restriction on the mounting freedom of the semiconductor device on the board, which is dependent on the design of the shield casing.
Consequently, it has been suggested that areas other than a light-receiving area of the infrared transmitting resin are covered with a conductive resin instead of the shield casing, and a lead frame protruding from the end portion of the infrared transmitting resin is electrically connected to the conductive resin (see, e.g., JP H09-84162 A).
In the conventional example, however, the electrical contact between the lead frame and the conductive resin tends to be insufficient, and consequently the shielding effect also tends to be insufficient, disadvantageously.